The present invention relates to electric generators, and in particular, to generators of a type which generate discrete electric pulses.
Many devices and uses exist for which it is necessary to generate a high-energy electrical pulse. The spark ignition of a conventional internal combustion engine is possibly the best known such use. There are many other well established though less familiar applications for high-energy electrical pulses. For example, electrical discharge machining utilizes a stream of discrete electrical pulses to generate sparks across a gap filled with a non-conductive liquid between an electrode and a metal workpiece, thus eroding the workpiece to a desired shape. Pulse welding welds metals with the intense heat of electrical pulse discharges. Many furnaces and similar devices use electrical pulses to ignite a fuel and thus obtain greater efficiency over a steady burning process. The synthesizing processes for certain chemicals utilize electrical pulses. The list goes on and on.
Various conventional devices exist for generating electrical pulses, each sufficient for a certain class of applications. For example, a magneto coupled to a breaker circuit and high-voltage transformer has been used to generate the necessary ignition spark in small internal combustion engines. Larger engines, such as found in automobiles, typically use a battery in place of the magneto, and more modern engines have replaced breaker points with electronic switches.
Relatively low-energy electrical pulses can be generated entirely with integrated electronic circuitry, and various circuit designs exist for this purpose. As the required energy of the pulse increases, designing a suitable electronic module for pulse generation becomes increasingly difficult. It is possible to add discrete components such as capacitors and inductors to increase the energy of the pulse, but even such components have practical size and power limitations.
In addition to purely electronic pulse generators, there are various electro-mechanical devices which can be used to generate pulses. The magneto is a simple example of such an electromechanical device. In general, these devices convert some form of mechanical energy, such as the inertia of a rotating member, into electrical energy through the use of an electromagnetic field.
The generation of an electrical pulse may be viewed as a matter of concentrating electrical energy in a short time interval. An electronic device draws energy initially from a line voltage source or from a battery. Given sufficient time, an arbitrary amount of energy may be obtained. Similarly, an electromechanical device generally draws energy from the kinetic energy of a moving mass, which is converted to electrical energy. Given sufficient time, this too can supply an arbitrary amount of energy. Generating a pulse amounts to storing and discharging the energy in a sufficiently short time interval. The greater the energy storage required and shorter the time interval of discharge, the more demanding are the design constraints for an electrical pulse generator.
Although various conventional devices exist for the generation of electric pulses, there are yet potent needs for improved pulse generation devices. As in any apparatus, improvements might take the form of reduced cost of manufacture, higher reliability, lower energy consumption or operating cost, etc. But there is specifically a need for devices capable of supporting larger energy discharges, and/or which concentrate the discharge in shorter time intervals, than conventional pulse generators of comparable size, power input, and other characteristics.
Higher energy/shorter pulse electric pulse generators would have manifest utility as replacement for current pulse generators in any number of conventional applications. For example, a higher energy pulse generator used as an ignition source in an internal combustion engine might provide more complete fuel combustion, or greater ease of starting in cold or similar adverse conditions, or permit the use of alternative fuels, or operate more effectively in the presence of electronic noise, or free some other design constraint, so that the engine is made more fuel efficient, less costly to operate, more reliable, or in some other sense improved, over a comparable internal combustion engine using conventional spark ignition means. Similar observations can be made for many of the current conventional applications for electric pulse generators.
Even greater potential use for improved electric pulse generators could lie in applications which don""t yet exist, or if they exist, exist only ephemerally in laboratories. Some applications of this variety have the aura of science fiction, yet it must be remembered that yesterday""s science fiction has often become today""s commonplace reality. At least part of the reason that many such potential applications have not yet achieved actual embodiment is that practical means for generating electrical pulses of sufficiently high energy and short duration are currently unavailable. An improved, high-energy pulse generator may provide the crucial link in the development of practical, working devices of this genre.
One example of such a futuristic application is the rail gun. A rail gun is a device which accelerates an object to a high speed using a very high-energy pulsed electromagnetic field. Although it is sometimes associated with military applications, it could be used various other purposes, such as launching satellites. Although theory says that such a device is possible, a practical, working device for, e.g. launching a small satellite, would require an electrical pulse of enormous energy, such as would be difficult or impossible to generate using conventional techniques.
Another such futuristic application may lie in the field of controlled nuclear fusion. Nuclear fusion requires a very high catalytic temperature, and at least some research has suggested that an electric pulse of sufficiently high energy and short duration might be used to help provide the necessary triggering conditions. Again, a pulse of this type would be difficult or impossible to generate using conventional techniques.
In sum, improved, more powerful, electric pulse generators could not only enhance the performance, cost or other characteristics of conventional devices which use pulse generators, such as spark ignition internal combustion engines, but open up entirely new frontiers only vaguely, if at all, imagined. Researchers in the field have not been ignorant of these needs, and a variety of proposed and implemented pulse generator designs have been produced. But existing designs have limitations that preclude a greater utility. A clear need exists for improved pulse generation techniques.
In accordance with the present invention, an electric pulse is generated by a moving multi-pole electromagnetic device in which the poles have a pseudo-random distribution, such that the poles periodically align. The device is capable of producing a brief pulse when the poles align, and at other times during the rotation produces little or no electrical output.
In the preferred embodiment, an equal number of poles exist on the rotor and stator, and all poles are equally sized and are spaced at equal circumferential intervals around the axis of rotation. However, unlike a conventional generator in which the polarity of poles alternates in a simple pattern, the polarity of the poles in accordance with the preferred embodiment varies in accordance with a pseudo-noise pseudo-random binary sequence function. At one point in the rotor""s revolution, all rotor poles are aligned with corresponding stator poles to provide maximum net magnetic flux through the armature windings. At all other angular positions of the rotor, the rotor and stator poles are misaligned so that the net flux through the armature windings is small. In operation, rotation through the misaligned angular positions of the rotor produces essentially no flux change so that no electric power is generated. When the rotor reaches the aligned position, there is a sudden, large flux change which generates a high-energy electric pulse.
In the preferred embodiment, the pseudo-random distribution function assignment of polarity to the poles is accomplished according to a primitive polynomial spreading code xe2x80x9cm-sequencexe2x80x9d. In this embodiment, the number of poles in each of the rotor and the stator is (2Nxe2x88x921), where N is a positive integer greater than 1. Both the rotor poles and the stator poles follow the same sequence. The primitive polynomial spreading code m-sequence has the property that it correlates to itself in only one cyclic phase and has almost no correlation in all other cyclic phases. Thus, as the rotor rotates through (2Nxe2x88x922) of the (2Nxe2x88x921) pole positions, the net flux through the windings is (xe2x88x921) units, where a unit is the flux produced by a single pair of aligned poles. I.e., there is virtually no correlation between rotor poles and stator poles (xe2x80x9cpseudo-randomxe2x80x9d) in these (2Nxe2x88x922) pole positions. In the remaining pole position, all the poles are aligned, and the net flux is (2Nxe2x88x921) units. Thus, there is a sudden, large flux change when the rotor reaches the aligned position.
Various alternative arrangements of coils and magnets are possible. In a first preferred embodiment, the rotor poles are permanent magnets of polarity assigned by the pseudo-random distribution function, while the stator poles are electromagnetic coils similarly assigned. In a second preferred embodiment, both the rotor poles and the stator poles are electromagnetic coils, the field winding being on the rotor, and the armature winding on the stator. In a third preferred embodiment, both the rotor and stator poles are electromagnetic coils, the armature winding being on the rotor and the field winding on the stator. In a fourth preferred embodiment, the stator poles are permanent magnets, while the rotor poles are electromagnetic coils.
In one alternative mode of operation, the drive field is provided by an electromagnetic coil driven by an AC source. At a relatively low rotational frequency, the device behaves like a pulsed or switched transformer in which most of the energy is supplied by the AC source, while at higher rotational frequencies the AC drive component is less significant.
In one exemplary application, a pulse generator in accordance with the preferred embodiment is used to generate an ignition spark for an internal combustion engine. However, many other potential applications are also possible.
An electric pulse generator constructed in accordance with the preferred embodiment of the present invention has the potential to generate a high-energy, short duration pulse beyond the capabilities of conventional pulse generators of comparable size and operating characteristics, and could be used in a variety of applications, now known or hereafter developed.